He was a wealthy and powerful partner at the mighty Wall Street firm, Lazard Freres & Co., the financial world’s leading dealmaker, and had just led an effort to save New York City from bankruptcy.

Presidents and potentates took his call, and cabbies – believing the then 47-year-old titan had saved their lives along with the city’s – refused to accept his money when they drove him around town.

But just before Christmas, Rohatyn found himself on a jet to Paris.

Helene Gaillet de Barcza, his mistress of about eight years, was having a major showing of her photographs in the City of Lights, and Rohatyn didn’t want to miss it.

In fact, she says, Rohatyn had finally agreed to divorce his wife of 19 years and get married later that month at a church on the top of Alta Mountain, in France.

The joy didn’t last.

When de Barcza – now Helene Gaillet de Neergaard – returned to New York City to the penthouse the two shared in the Hotel Alrae, she discovered Rohatyn had moved out.

“I came back to a totally empty apartment,” she said. “There was only my clothes left, and the furniture of the hotel. And I had no forwarding address.”

De Barcza called Rohatyn’s office, but his secretary blew her off. Days later, the secretary called her back and said Rohatyn would like to meet at the “21” Club. “And so I got all dressed up,” she said, expecting the up-and-down romance would again take a turn for the better.

But no dice.

Over dinner, Rohatyn dropped the bomb. “I have to move on with my life,” he said, according to de Barcza. “I need more space. I love you, but I have to do something else.”

Little did de Barcza know that Rohatyn had already started dating another woman, Elizabeth Vagliano, whom he would marry in 1979, when he finally divorced his first wife, Jeannette.

Rohatyn’s womanizing and various affairs are laid bare in the just-released book, “The Last Tycoons,” by William D. Cohan, a journalist and investment banker who spent six years at Lazard.

Reflecting two years of exhaustive research, Cohan’s 671-page book pokes around every nook-and-cranny, it seems, of Lazard’s long history, from its role as the leading Wall Street adviser for decades to its takeover by Bruce Wasserstein.

No one plays a larger role in the book, though, than Rohatyn – and his brilliance at getting deals done is on display.

But Rohatyn’s womanizing, affairs and political tin ear are also examined.

De Barcza, who talked in depth to Cohan about her affair with Rohatyn – whom she refers to, in her slight French accent, as Fay-leex – lays public Rohatyn’s very private side.

She said Rohatyn asked for weeks for a date before she finally agreed to go for drinks. Drinks led to dinner. Dinner led to Rohatyn asking to go back to her place. Again, she turned him down for weeks until, she told Cohan, “her resistance broke down.”

“But at that time, I did wonder to myself why am I doing this, knowing that he was very, very much married and knowing that it was never going to lead to anything for me,” she told Cohan.

“And I wasn’t in love with him. He was not in love with me. It was not even a great affair. You know what I’m saying? It was just something that was happening. But in a sense, I enjoyed having an affair with him, because we always had dinner, and that was always the interesting part, the conversation.”

And De Barcza wasn’t the only woman with whom Rohatyn was fooling around. De Barcza said that during their trysts at a 62nd Street pied-à-terre, she spied lipstick and earrings that did not belong to her.

And by no means was Rohatyn’s womanizing restricted to his love nests.

Cohan reports that one day in the 1970s, Lazard’s top dog, André Meyer came looking for Rohatyn only to find his office locked in the middle of the day. After knocking on the door twice and getting no answer Meyer yelled, “loud enough to be heard around the floor,” the book says, ” ‘Felix, why don’t you go to a hotel room like the rest of the partners!’ ”

One rumor had Rohatyn in the locked office with his secretary. Another had that the second person was movie star Shirley MacLaine.

“I told Rohatyn that the office incident was his Joey Buttafuoco moment,” Cohan told The Post. Rohatyn, among the wealthiest and most powerful figures in the city, was also linked romantically to Jackie O and Barbara Walters.

As successful as Rohatyn was in business and with women, the finance king was just as clumsy with his political aspirations – to go to Washington and become the Secretary of the Treasury.

A Democrat at the height of his power in the late 1970s, Rohatyn had to weather 12 years of Republicans in the White House before attempting to pursue his dream of becoming the top dog at Treasury.

But Rohatyn bungled his chance – nearly ignoring candidate Bill Clinton during a visit to Lazard’s offices in 1992, refusing to raise money for Clinton and then backing former Lazard client Ross Perot.

“He is absolutely tone deaf when it comes to politics,” Cohan said in a telephone interview last week. richard.wilner@nypost.com